Lubricating composition



Patented Oct. r, 1941 UNHED STATES LUBRICATING COWOSITION Reginald G.Sloane, Elizabeth, N. 3., assignor to Standard Oil Development Company,a cornotation of Delaware No Drawing. Application October 3, 1933,Serial No. 692,030

5013M The present invention relates to improved 1 lubricating oils andmore specifically-to oils of high stability both toward oxidation andsludge formation as in .a continuation-in-part of the previousapplication Ser. No. 408,421 filed No vember 19, 1929, now Patent No.-1,966,050 issued July 10, 1934. The invention will be fully understoodfrom the following description.

It has been observedthat after lubricating oils have received a highdegree of refinement they are often more unstable particularly towardoxidation than the impure or crude cutsirom which they were obtained.Thereason for this is thought to be that the refining process removessubstances which act as inhibitors of oxidation. Furthermore, inhibitorsof this type are known suchas the cresolsand naphtholswhich when addedin relatively smau'amounts to lubricating oils showing a high oxidationrate cause a considerable reduction.

The present invention relates to a new class. of inhibiting substanceswhich are considerably more powerful than thosepreviously known.

This new class of inhibitors comprises in its broadest sense aromaticsulfur compounds in which the sulfur atom is attached directly to a"carbon atom. These suiistances make up a rather large class and the-onesof special commercial value are'those boiling above 150 C. orpreferablyevemhigher, say. above 180 or 200 C., and

able but the other groups mentioned, while not particularly desired, donot destroy the effect of the mercaptan or disulfide groups. In the samemanner carboxyl, aldehyde and keto groups may be present. It will beunderstood that the compounds containing only carbon, hydrogen andsulfur are preferred, particularly disulfides and mercaptans.

While the above description has been limited entirely to sulfurcompounds, it should be understood that in each case selenium ortellurium may be substituted for the sulfur atom, but for reasons ofeconomythe sulfur derivatives are preferred. It is also usually the casethat the sulfur compounds are more active.

The oils in which the present inhibitors are to be used are moreespecially those which are substantially parafilnic in type, forexample,

has a maximum absorption rate in excess of which for this reason willnotbe lost during the use of the lubricant at such temperatures as arelikely to beencountered in the lubrication of automotive engines. or thelike. Aromatic disuliides. and mercaptans may be used such as phenyl,cresyl or higher al blated disulfides, mercaptans and the correspondingnaphthyl or anthryl, phenanthryl derivatives or their alkylated productsand the relative pomtions of the sulfur and alkyl groups in the ringsare of only minor significance, all being of good inhibiting power.,More than one-jsulfur atom may be attached to a single ring if desired,as in the di or tri thio-phenols, cresols and naphthols.

All of the substances mentioned .above consist only of the elementscarbon, hydrogen and sulfur or, in other words, they are sulfurizedhydrocarbons, and while these are generally preferred other elements maybe present in the molecule without disadvantage, for example, oxygen ornitrogen and similar elements. As examples of such materials can bementioned aromatic disulfides and mercaptans containing hydroxy,

, nitro, amino, azo and hydrazo groups. The presence of the hydrow groupis particularly desir- 55 about 50 cc. of oxy en per fifteen minuteinterval per 10 cc. of sample when agitated with oxygen at a temperatureof about 200 -C. The rates of oxidation for well refined oils of thetype mentioned above may beffar in excess of the figure mentioned, forexample, they may be up to 100 or 180 cc. absorption or even up to 300cc.

in very pure parafilnic oils.

Other classes of oils in which the improved inhibitors are of greatadvantage are the highly refined white oils produced by the actionoffuming or concentrated sulfuric acid. and also destructivelyhydrogenated oils or oils prepared by strong hydrogenation at lowtemperatures.

While the inhibitors mentioned above are of the greatest advantage withoils listed la the previous paragraphs because of their high oxidationrate, they have also been found to be so powerful as to likewise show aconsiderable reduction in the oxygen absorption rate of lower grade oilsof more or less naphthenic or ,asphaltic types such as the Coastal orCalifornia oils which are characterized by a viscosity index below 50-or even 30 and by oxidation rates of the order of 30 cc. in the unitsmentioned above. It may well be that the action of the presentinhibitors is difierent from the ordinary naphtholic or cresolicinhibitors, since these latter show substantially no effect whatever onthe naphthenic types of oils. on the other hand, the present inhibitorsreduce the oxidation rate to a considerable degree, for example, by asmuch as one-half. It should be noted, however, as stated above, that theinhibitors are not of greatest value in connection with these oils sincetheir oxidation rates are already low.

The amount of the various inhibitors which may be used depends upon theoil to which it is to be added, the particular inhibitor, and also tothe conditions which are likely to be encountered. In general thesubstances are considerably more powerful than cresols or naphthols andfor this reason may be used in smaller quantities. It may be said thatif the oil is designed to stand higher temperatures, the amount of theinhibitors should be increased. The new inhibitors are effective whenused in amounts as little as .01% in the case of very highly refined oilsuch as white oil or other less highly refined oils when used in thelower temperature range, for example, under 150 C., but ordinarily moreis desired, for example .05 or .10%, or in some cases even more. Of thevarious compounds the disulfides are preferable to mercaptans becausethey have a less objectionable odor.

As illustrations of the materials used and their action in variouslubricating oils, the following examples are given:

Example I A well refined lubricating oil having a viscosity ofapproximately 145 seconds Saybolt at 100 F. is blown with a steadyvolume of air, 10 cu. ft. per hr. at 300 F. (149 0.). The sample was 300gr. At intervals the free acid was determined by titration with alkali.The following table gives the rate of acid formation with time, inrespect to the Blank sample containingno inhibitors, and the same oilcontaining specific inhibitors.

Acidity-MgKOH per qt. of oil Tlme 11mm 1 4% tbio 3% thio 3% di- Blankbeta beta (figienyl naphthol nsphthol ulilde Oxygen absorption .1% of amixture of the last two .l% dimereapto diphenyl .1% alpha naphtholdisuliide Blank thio WWWN HHD-IN Owen l-nlbmlm The present invention isnot to be limited by any theory of the reaction of oxidation orinhibition thereof, nor to any particular inhibitors or oils containingthem, but only to the following claims in which it is desired to claimall novelty inherent in the invention.

I claim:

1. The combination, with a highly refined viscous mineral oil, of asufficient quantity of a disulfide of an aromatic compound containingonly the elements carbon, hydrogen and sulfur, to reduce substantiallythe tendency of the oil to form acidic material through oxidation.

2. The combination, with a highly refined viscous mineral oil, of asuflicient quantity of diphenyl disulfide to reduce substantially thetendency of the oil to form acidic material through oxidation.

3. A composition of matter comprising a petroleum lubricating oilcharacterized by a high initial rate of oxidation containing dissolvedtherein, in an amount suflicient to reduce substantially the tendency ofthe oil to form acidic material through oxidation, an oxidationinhibitor selected from the class consisting of alpha and beta naphthylmercaptans.

4. The composition of matter according to claim 3, in which theinhibitor is beta naphthyl mercaptan.

5. A composition of matter comprising a white mineral oil obtainedby.strong acid refining containing dissolved therein, in an amountsufllcient to reduce substantially the tendency of the oil to formacidic material through oxidation, beta naphthyl mercaptan.

REGINALD G. SLOANE.

